problem analysis 2

List of problems:
\begin{itemize}
\item storing a whole index on a single node 
\item problem of information retrieval. Why we use ranking
\item problem of distribution. Setting requirements for it. Individual data items will need to be accessed for changing rank. Moreover,  for tagging  untagging? Also, how can we make search efficient?
\item problem if expansion/retraction volatility if only one threshold is used. (solution: we use 2 thresholds)
\item problem of retraction. Given the distribution, a parent cannot know the size of its children, so how does it know when to contract?
\item problem of merging results at the requester. 
\item Problem of finding intersections for multiple queries. 
\item Scalability of search. How can we ensure that search latency does not grow two much in relation to the size of an index? (caching)
\item Malicious users flooding system with queries. TTL
\end{itemize}

